Brit hosted a charity event in LA on May 11 and looked stunning in a skin-tight bandage dress! Beverly Hills based fitness expert adds Britney lost the weight in a ‘healthy way.’

Whoa, Britney Spears — where have you been hiding?! The 29-year-old singer slipped on a body-skimming electric yellow Herve Leger dress and had us rubbing our eyes in disbelief.

“Britney lost somewhere between 15 and 20 pounds and you can see it clearly in her hips thighs and even her bust and arms,” Steve Jordan an LA based trainer and owner of Acceleration gym tells HollywoodLife.com. “You can see in her chin and jaw line look much more defined. Britney lost weight everywhere she needed to. Your body takes weight off where you put it on.”

We completely agree — Brit was much heavier during her March 26 GMA performance of her hit new single “Hold It Against Me.” But we were floored when she debuted her newly toned and slim figure at her Evening of Southern Style Event for The St. Bernard Project with her dad Jamie Spears and her longtime boyfriend Jason Trawick. Even some of her A-list friends stepped out to support her like Kim Kardashian, Selena Gomez and Kelly Osbourne!

“Obviously Britney has been working on getting prepped for her tour. Burning and moving a lot. Calories in … calories out,” Steve says. “This looks very healthy. Such a glow about her. Someone who loses it unhealthy doesn’t have a glow like she does.”

If you’re wondering how Brit shed the excess pounds, she didn’t do it by starving herself.

“She definitely did it with cardio. Just knowing a little history of Britney, I’m sure she was doing the elliptical, treadmill, and might have incorporated boxing,” Steve tells us. “She was doing high energy to lose that kind of weight and look as good as she does. She looks proportioned, and had to be using her upper and lower body.”

The old Brit has been slowly but surely coming back with the release of her new album Femme Fatale. But we couldn’t have imagined that she’d ever look as good as she did in her “Hit Me Baby” days. It’s been six years since we’ve seen Britney look this good!